Greases are widely used in various machines and tools such as automobiles, electric.electronic machines and instruments, construction machinery, industrial machinery, machine tools, information-systems, and also parts as their structural components. Recent trend towards making these machines and tools work faster together with more size reduction, higher performance, and lighter weight, etc., inevitably makes the temperatures of the peripheral machines and tools higher and higher. To meet the requirements for lighter weight, lower cost, tighter sealing, etc., molding products of resins or rubber have been much more used, and also to meet the requirement for further quietness improvement, much tighter sealing is desired.
The metallic parts are often to be exposed to the atmosphere of corrosive gases generated from components, etc. contained in resins or rubber, for example, a sulfide gas, a hydrogen chloride gas, a sulfer dioxide gas, ammonia, oxygen, etc., due to such use conditions as higher temperatures and tighter sealing and are also often to be exposed to such corrosive gases permeated from the outside due to severe use conditions.
To solve such problems, it has been proposed to use a grease comprising a fluorosilicone oil and a fluoro resin to suppress hydrogen sulfide permeation and prevent corrosion of contact materials. Besides the fluorosilicone oil, it is said that such fluorine-containing compounds as fluorocarbon, fluoro ester, fluorine-modified paraffin oil, fluorine-modified ester oil, etc. also have the similar effect. However, not all of these fluorine-containing compounds have the effect on the suppression of hydrogen sulfide permeation at the same degree. In this connection, it should be noted that the fluorosilicone oil can suppress the hydrogen sulfide permeation, but has a poor abrasion resistance, resulting in abrasion of contact materials. The fluoro ester, fluorine-modified paraffin oil, and fluorine-modified ester oil have a poor heat resistance, and thus cannot be used in a higher temperature atmosphere as a problem.
Patent Literature 1: JP-A-59-189511
As to the fluorine-based grease, it has been proposed to use a fluorine-based grease comprising a perfluoropolyether oil having repeating units, represented by (CF2CF2CF2O)n′ as a base oil to improve the heat resistance and chemical resistance, where no reference is made to the permeation resistance to the corrosive gases.
Patent Literature 2: JP-B-2-32314
Another fluorine-based grease having distinguished wash-ability, abrasion resistance, leakage resistance, etc. has been also proposed, where no reference is also made to the corrosion resistance to corrosive gases, in this case.
Patent Literature 3: JP-A-2001-354986